The present invention relates to an improvement in a scroll compressor adapted to discharge fluid, such as a fluid refrigerant compressed in a pair of compression spaces through discharge openings at the same time.
Generally, a scroll compressor has an orbiting scroll member which is substantially in an involute curve and attached to one surface of the end plate in an upstanding position, and a fixed scroll member which is formed complementary to the orbiting scroll member and is arranged in juxtaposed relation with the wraps of the two members being fitted closely together. The orbiting scroll member is moved in an orbiting motion while the rotation thereof on its own axis is inhibited by an Oldham's ring disposed between, for example, the orbiting scroll member and a main frame or a housing. The orbiting movement of the orbiting scroll member reduces the sealed space or fluid pocket defined by the two scroll members, and thus compresses a gas therein to increase its pressure. The general structure and operation of the scroll compressor are shown in, for example, U.S. Pat. Nos. 4,759,696; 4,838,773; and 4,886,434, all assigned to the present assignee.
In the conventional scroll compressor, the compressed fluid refrigerant in the compression space is exhausted at the time when the compression space is connected to the discharge opening and, accordingly, the compression ratio is determined by the number of wrap involution and the size of the discharge opening. Consequently, when refrigerants with different evaporation temperatures are used, additional suitable compressors for the different, temperature refrigerants must be employed. Thus, an attempt has been made to provide a discharge valve in the discharge opening so that the compression ratio can be changed in accordance with the difference in evaporation temperatures of the refrigerants, as shown in Japanese Patent Publication No. 63-58271, published Nov. 15, 1988.
However, in the conventional compressor shown in the above-stated Japanese Patent Publication, the change of compression ratio by means of the discharge valve to the discharge opening has the disadvantage of discontinuity in the refrigerant flow from the compression space to the discharge port and consequently the discharge valve is repeatedly opened and closed during operation thus producing noise. A discharge opening of larger diameter requires a valve of larger thickness, with the result of producing greater noise by repeatedly opening and closing the valve. Further, when the scroll compressor unit is reversely rotated, the discharge opening is closed by the discharge valve with the result that the compression space is placed under a vacuum, and the pressure difference between the compression space and sealed container of the scroll compressor causes abnormal, forcible engagement between the fixed scroll member and the orbiting scroll member, with the result of seizing.